In recent years, surface light sources with high luminous efficiency that include electroluminescent elements such as light emitting diodes (LEDs: Light Emitting Diodes), organic EL (Electro-Luminescence), and the like have attracted attention. An electroluminescent element is formed of a light emitting layer sandwiched between a flat cathode and a flat anode. Generally, the anode is often formed of a transparent electrode, and the cathode is often formed of a metal reflective electrode. When the cathode is formed of a metal reflective electrode, light is extracted through the transparent anode, and such an electroluminescent element is used as a single surface emission-type light emitting device.
Japanese Laid-Open Patent Publication No. 10-294182 (PTD 1), Japanese Laid-Open Patent Publication No. 2012-15122 (PTD 2), and Japanese Laid-Open Patent Publication No. 2011-65781 (PTD 3) disclose electroluminescent elements used as transparent surface-emission light sources, in which transparent electrodes are used for both a cathode and an anode.
In such an electroluminescent element in which transparent electrodes are used for both a cathode and an anode, plasmon absorption loss that occurs when a metal reflective electrode is used on one side is reduced, and thus, a more efficient electroluminescent element can be realized. Such a transparent electroluminescent element can have a variety of designs, and is suitable for making the space seem expansive.